In many applications in which use is made of data transmission networks there is the desire or even the necessity to ensure a fault tolerance which is as high as possible. For this purpose, habitually parts of the networks, i.e. at least the essential network components, are constructed redundantly or even the entire network is constructed redundantly. For example, if a data transmission network comprises a server providing data to other network devices or entities, one or more further identical or essentially identical servers can be provided which, in the case of a failure of the former server, can take over its tasks.
One example for data transmission networks, in which servers are used and in which a high fault tolerance is absolutely required, are automation or communication systems of vehicles, such as, e.g., aircraft. These data transmission networks are often configured as Ethernet networks, which may have, amongst others, a star-type configuration.
One example for an Ethernet based data transmission network in aircraft is the cabin management system of aircraft of the types Airbus A380 and A350. In these aircraft the Ethernet standard 10baseT having a data rate of 10 Mbps is employed, and two or three redundant servers are provided, one or two of which serve as failover for the server operating during normal operation. Due to the relatively low data rate it is possible to couple the servers into the network by a passive coupling device in the form of a simple T-connector.
However, in case higher data rates are to be used, such as, for example, a data rate of 100 Mbps according to the Ethernet standard 100baseT, the coupling by T-connectors is no longer suitable. Instead, as a rule an active coupling device, such as a network switch, is used in order to functionally couple the servers to or into the data transmission network. Due to their active construction, as compared to simple and passive T-connectors such coupling devices are, however, much more prone to errors, so that the fault tolerance of the network as a whole is significantly reduced by their use. Generally, similar considerations also apply for differently configured Ethernet data transmission networks and for data transmission networks not operating in accordance with the Ethernet standard.
Due to this fact data transmission networks, such as, for example, data transmission networks which are utilized in aircraft as, e.g., part of the cabin management system, are often constructed or configured redundantly in their entirety. In other words, several separate physical networks are provided, and the data transmission is taking place in parallel in all networks. In general and in particular in aircraft it is desirable to keep the hardware expenditure and the complexity of the system as low as possible and to nevertheless ensure a high fault tolerance.